During development, the nervous system is vulnerable to chemical agents present in the environment. For instance, children exposed to lead are at risk for cognitive and emotional problems contributing to lower IQ and antisocial behaviors. Today, the level of exposure to lead is still significant for children in urban, industrial and rural areas, and the intensity and frequency of violent acts performed by adolescents in America is particularly troubling. Various animal models are being developed to better understand the developmental effects of lead on cognition. However, little is known of the neurobiology underlying impairments in social and emotional behavior. The present studies were designed to test the effects of early exposure to lead on aggressive behavior and stress responsiveness in an animal model. Golden hamsters are ideal for these studies as their aggressive behavior has been well characterized. Furthermore, the neurobiology of aggression is also well understood in this species. The following topics are covered under the following studies. First, the proposed studies will determine the effects of exposure to various doses of lead on aggressive behavior and stress responsiveness in golden hamsters. These two topics will be studied together as they appear to be linked. Second, the proposed studies will tests the effects of lead exposure on the neurobiology underlying aggressive behavior and stress responsiveness, focussing particularly on the serotonin system. Third, the studies will test the effects of lead exposure on the neural systems controlling aggression and stress responsiveness. Together, these studies will provide a preclinical database that may contribute to a better understanding of risk factors and potential therapies in human populations.